Named tuple from struct
Is is possible to get a named tuple from a struct type?
E.g.:
struct S { int foo; string bar; }
S s;
S.tupleof t; // S.tupleof is a tuple type, as opposed to s.tupleof,
// which yields a tuple instance
t[0] = 1;
t.bar = 2;
If not, I think it would be quite useful.
Even still, a way to describe tuple types as if it was a struct would also
be useful:
tuple StructLike
{
int foo;
string bar;
}
StructLike t;
t[0] = 1;
t.bar = 2;
--
Atenciosamente / Sincerely,
Guilherme (n2liquid) Vieira
Re: auto declarations
Ellery Newcomer: int a = 1, *b = null; Walter has disallowed code like this in D because in C it is a well known source of bugs (so much that C style guides strongly suggest to declare only each variable in a distinct statement and line of code). auto a = 1, b = null; I have discussed this with other people some time ago. At first I don't like this, it's against the D rule of not allowing different types to be initialized in the same statement. It may cause some bugs. Example: if you write a line of code like, meaning it to initialize six double variables both you have a bug: auto x1=1., x2=2., x3=3., x4=4., x5=5, x6=6.; But you are playing with fire. Better to be safer and write: double x1=1., x2=2., x3=3., x4=4., x5=5, x6=6.; Or even: double x1, x2, x3, x4, x5, x6; x1 = 1.0; x2 = 2.0; x3 = 3.0; x4 = 4.0; x5 = 5.0; x6 = 6.0; Or: double[6] x; foreach (i, ref xi; x) xi = i + 1; Or: double[6] x = array(iota(1.0, 7.0)); The first is accepted by dmd, and it should result in typeof(a) == int and typeof(b) == void*. It is somewhat contradictory to the error message resulting from the second: multiple declarations must have the same type, not int and int* Error messages in DMD are a draft :-) I have opened many bug reports that suggest to improve them. Here the error message is not fully correct, but I think it's acceptable. To improve it the D compiler may also give a number of the error, and a manual of the errors may explain that indeed the auto is allowed to instantiate different types, etc. I don't know why DMD errors are not numbered ad in C#. Bye, bearophile
Re: Named tuple from struct
On 2011-01-08 09:15, Guilherme Vieira wrote:
Is is possible to get a named tuple from a struct type?
E.g.:
struct S { int foo; string bar; }
S s;
S.tupleof t; // S.tupleof is a tuple type, as opposed to s.tupleof,
// which yields a tuple instance
t[0] = 1;
t.bar = 2;
If not, I think it would be quite useful.
You cannot get only the names as a tuple but you can implement something
similar:
1. Loop through the tuple
2. Get the name of a field in the struct using the stringof property
on the tuple
3. Slice of the name of the struct and some other unwanted characters
You can have a look at this method as well:
http://dsource.org/projects/dstep/browser/dstep/objc/bridge/ClassInitializer.d#L84
Even still, a way to describe tuple types as if it was a struct would
also be useful:
tuple StructLike
{
int foo;
string bar;
}
StructLike t;
t[0] = 1;
t.bar = 2;
--
Atenciosamente / Sincerely,
Guilherme (n2liquid) Vieira
--
/Jacob Carlborg
Calling anonymous delegate recursively ?
eg. to return a fibonacci delegate:
return (ulong m) {
if(m 2) return m ;
return _self_ref(m-1)+_self_ref(m-2) ;
} ;
Is it possible? Thank you!
Re: Calling anonymous delegate recursively ?
On 01/08/2011 04:45 PM, tsukikage wrote:
eg. to return a fibonacci delegate:
return (ulong m) {
if(m 2) return m ;
return _self_ref(m-1)+_self_ref(m-2) ;
} ;
Is it possible? Thank you!
http://en.wikipedia.org/wiki/Fixed_point_combinator#Y_combinator
I don't think there's a built in way to self-recurse.
Re: Calling anonymous delegate recursively ?
As a workaround you can do this for now:
import std.stdio;
enum deleg = returnFib();
ulong delegate(ulong m) returnFib()
{
return (ulong m)
{
if(m 2)
return m;
return deleg(m-1)+deleg(m-2);
};
}
void main()
{
writeln(returnFib()(10));
}
Otherwise I'd really like the ability for a lambda to call itself.
Perhaps a feature request is in order.
Re: Calling anonymous delegate recursively ?
On 08/01/2011 16:00, Pelle wrote: snip http://en.wikipedia.org/wiki/Fixed_point_combinator#Y_combinator snip How are you getting around D not supporting recursively defined types? Stewart.
Re: Calling anonymous delegate recursively ?
On 08/01/2011 17:40, Andrej Mitrovic wrote: snip Otherwise I'd really like the ability for a lambda to call itself. Perhaps a feature request is in order. I'm not sure what D would gain in practice. If you want a function that calls itself, why not just name the function? Stewart.
Re: Calling anonymous delegate recursively ?
On 1/8/11, Stewart Gordon smjg_1...@yahoo.com wrote: On 08/01/2011 17:40, Andrej Mitrovic wrote: snip Otherwise I'd really like the ability for a lambda to call itself. Perhaps a feature request is in order. I'm not sure what D would gain in practice. If you want a function that calls itself, why not just name the function? Stewart. I don't know. Perhaps it would be useful in generics..
Re: Calling anonymous delegate recursively ?
Thank Pelle , and others.
I'm thinking ways to do this task :
http://rosettacode.org/wiki/Anonymous_recursion
With this last version of Y-combinator
http://rosettacode.org/wiki/Y_combinator#D ,
it look like this:
ulong fib(long n) {
if(n 0) throw new Exception(No negative) ;
return Y((ulong delegate(ulong) self) {
return (ulong m) {
return (m = 1) ? m : self(m-1) + self(m-2) ;
} ;
})(n) ;
}
and works. Only that this Y-combinator seems induced a lot of
overhead(four return statements in the Y's definition).
From D document, if i not misunderstood, a delegate has 2 property .ptr
(frame pointer) and .funcptr (address of function), so the delegate
should be a structure? Would there be a hack to get access to this
structure? It seems not now.
Thanks again.
Pelle wrote:
On 01/08/2011 04:45 PM, tsukikage wrote:
eg. to return a fibonacci delegate:
return (ulong m) {
if(m 2) return m ;
return _self_ref(m-1)+_self_ref(m-2) ;
} ;
Is it possible? Thank you!
http://en.wikipedia.org/wiki/Fixed_point_combinator#Y_combinator
I don't think there's a built in way to self-recurse.
Re: What's wrong with this code?
On Sat, 08 Jan 2011 20:34:39 +, Sean Eskapp wrote:
if(left == null)
1) write if (left is null) instead if checking for null. Equality
operator is rewritten to a.opEquals(b), which you don't want if you
checking for null.
this()
{
left = right = null;
}
2) default constructor as you written it is not needed, fields are always
initialized to default value of their type, which is in this case null.
private const Fib* left, right;
3) Classes in D are reference types. It should be
private const Fib left, right;
4) second constructor - Classes in D are reference types, operator is
not needed (see point 3), parameter left and right are already references
to class.
Re: What's wrong with this code?
Sean Eskapp napisał(a):
I had some code that was segfaulting, so I rewrote the basic idea as a
fibonacci function, and lo and behold, it still segfaults. Why, and how
to fix?
This looks fishy:
class Fib
{
private const Fib* left, right;
...
this(in Fib left, in Fib right)
{
this.left = left;
this.right = right;
}
Are you sure you want a pointer to class? Classes have reference semantics
in D (like Java). Structs are value types, though. Anyway, it looks like
the ctor takes the address of the reference placed on the stack.
--
Tomek
Implicit type conversion
Use case:
import std.variant;
void foo (Variant v) {}
void main () {
Variant v = 3; // ok, this () called
v = 3; // ok, opAssing called
foo (v); // ok, struct copy, this(this) called
foo (3); // error
}
I'm trying to understand what is needed to make this work from language
design perspective. Is there already known/proposed solution to make this
work? What comes to my mind as first - Variant constructor should be
called on last line, the same way as on the first. But maybe to solve
this, another operator is needed, opImplicitConvertFrom ...
Second question. Why is needed to have both - strut constructor (this)
and opAssing. In variant case, constructor just forwards to opAssing.
From high level point of view, I don't see any reason both should behave
differently...
Re: std.container.Array/RefCounted(T) leaking memory?
What method are you using to test the memory?
I'm puzzled that you've put a comment there rather than the code you're
actually
using.
I'm not using code, I'm checking the working set of my process in Task Manager,
and through every iteration, it adds 128 MB.
If you run this code twice, does the memory usage double?
Yes. I ran this code:
{
auto b = Array!(bool)();
b.length = 1024 * 1024 * 128 * 8;
}
{
auto b = Array!(bool)();
b.length = 1024 * 1024 * 128 * 8;
}
and Task Manager showed two increases of 128-MB.
Thank you!
druntime
where did libdruntime.a go in dmd.2.051.zip:/linux/lib ?
writef vs writeln and printing to the console
Unfortunately I can't provide a simple test case, but I have a case where using: writef(..\n); inside a loop that runs a dozen times does not print out each line as the statement is reached, instead it prints out everything at once when the application is done. If I use this: writeln(.); then I get each line printed out at the exact moment as this statement is reached. Is this normal behavior?
Re: What's wrong with this code? (OP)
Tomek got it right. Fixed by copying the objects, rather than using pointers. Thanks!
Re: druntime
On Saturday 08 January 2011 13:32:19 Ellery Newcomer wrote: where did libdruntime.a go in dmd.2.051.zip:/linux/lib ? I think that it's included inside of libphobos.a now, and has been for a few releases. The libraries are still separate, and you can build them separately, but from what I can tell, it looks like phobos ends up including the druntime stuff in itself when you build it. So, having a separate libdruntime.a would be kind of pointless unless you were specifically trying to avoid linking in any Phobos stuff, which would be highly abnormal, and in which case you could build druntime yourself. But Sean or someone else who's been involved in that build process may have a better answer as to what exactly is going on now and why. - Jonathan M Davis
Re: druntime
On 01/08/2011 09:02 PM, Jonathan M Davis wrote: On Saturday 08 January 2011 13:32:19 Ellery Newcomer wrote: where did libdruntime.a go in dmd.2.051.zip:/linux/lib ? I think that it's included inside of libphobos.a now, and has been for a few releases. The libraries are still separate, and you can build them separately, but from what I can tell, it looks like phobos ends up including the druntime stuff in itself when you build it. So, having a separate libdruntime.a would be kind of pointless unless you were specifically trying to avoid linking in any Phobos stuff, which would be highly abnormal, and in which case you could build druntime yourself. Figures, but I thought I looked in libphobos and didn't see druntime symbols.. oh well. And yeah, it's been a few releases since I've needed to build my own rpms
Re: druntime
On Saturday 08 January 2011 19:16:26 Ellery Newcomer wrote: On 01/08/2011 09:02 PM, Jonathan M Davis wrote: On Saturday 08 January 2011 13:32:19 Ellery Newcomer wrote: where did libdruntime.a go in dmd.2.051.zip:/linux/lib ? I think that it's included inside of libphobos.a now, and has been for a few releases. The libraries are still separate, and you can build them separately, but from what I can tell, it looks like phobos ends up including the druntime stuff in itself when you build it. So, having a separate libdruntime.a would be kind of pointless unless you were specifically trying to avoid linking in any Phobos stuff, which would be highly abnormal, and in which case you could build druntime yourself. Figures, but I thought I looked in libphobos and didn't see druntime symbols.. oh well. And yeah, it's been a few releases since I've needed to build my own rpms Well, I haven't actually gone so far as to look at the symbols in the library, but there is no libdruntime.a - only a libphobos.a - and it works. And if you build phobos, you still need to build druntime first. So, really, the only way that it could really work from what I can see is that libphobos.a includes the stuff from libdruntime.a in it. Why or how, I don't know. - Jonathan M Davis
Re: interface function overloading
== Quote from Jonathan M Davis (jmdavisp...@gmx.com)'s article
On Saturday 08 January 2011 22:01:11 %u wrote:
Isn't it possible to have a hierarchy in interface definitions such that it
is possible to overload according to best interface match?
This now won't compile due to multiple matches.
module main;
interface I1{}
interface I2 : I1{}
class C : I2{
this(){}
}
void func(I1 i){}
void func(I2 i){}
void main(){
func(new C());
}
Very little - if anything - in the way of overloading in D works by best
match. It pretty much always has to be exact or implicitly convertible and be
the _only_ option which is implicitly convertible. Sometimes, it can be pretty
annoying, but it's done to avoid cases where you accidentally call one
function
when you mean another, like you can get in C++ fairly easily.
Take a look at http://www.digitalmars.com/d/2.0/hijack.html
- Jonathan M Davis
I see, cast(ugly:) seems to work.
func(cast(I2)(new C()));
Thanks.
